Mycorrhizae are fungi, beneficial soil fungi, or more specifically, the roots of these soil fungi, which usually develop tiny myceliums. These tiny spores can be mixed into garden soil, where they then develop a fine network that wraps around the roots of plants growing in that garden soil. This covering acts as a kind of nutrient reservoir for the plant, the network actively sucks water and nutrients close to the roots, which in this symbiosis system do not reach the plant directly, but are “buffered” by the mycorrhizal fungus. As a result, the roots colonized by the mycorrhiza are supplied evenly and continuously, regardless of the weather. The result is that plants in particular that often suffer from root problems

Use mycorrhiza

If you are told that all you have to do is add mycorrhizae to your plants in order to do them some good, you better not take it lightly. There are basically different types of mycorrhiza and not every mycorrhiza helps every plant. Three large groups are traditionally distinguished:

  1. The ectomycorrhiza colonize the trees in our forests, they are typical for all trees belonging to the birch, beech, pine, willow and rose families. Ectomycorrhiza have long been used successfully in forestry to heal ailing trees growing in unfavorable locations. In the garden, they can help trees and conifers such as beech, birch, fir and oak to grow better. Because the ectomycorrhiza are formed, among other things, by our normal edible or poisonous mushrooms, it is quite possible that you can pick these mycorrhiza yourself in the forest if you inform yourself accordingly.
  2. The plant partners of the next group, the endomycorrhiza, are predominantly herbaceous plants. From the following plant families we now know that their species almost always live in symbiosis with a fungal partner. The heather plants (Erika and Co.), the wintergreen plants (e.g. the rare moss eye) and the orchids. The symbiotic fungi here are usually pillar fungi from the order of chanterelles, including anamorphic forms that cause fungal diseases in many other plants. In the case of orchids, the corresponding endomycorrhiza are said to be absolutely necessary for their development.
  3. The mycorrhizae most grown and sold for gardens and agriculture belong to the arbuscular mycorrhizae.

These arbuscular mycorrhizal fungi, or AM fungi for short, are the most common, oldest, and common of the mycorrhizal fungi. It is now believed that more than 80% of all land plants have a symbiotic relationship with AM fungi. This should include most herbaceous plants and most woody plants, as well as sweet grasses. In addition to grain, also lawn grass and bamboo.

Due to genetic studies, these AM fungi have just been systematically separated from the yoke fungi (zygomycota) and now form their own division of the glomeromycota. The most well-known arbuscular mycorrhiza grown for horticultural use is Glomus intraradices.

Which plants use arbuscular mycorrhiza?

Even if the area of ​​application seems almost unlimited at first, the sensible use of mycorrhiza is still more of a research area. The best way to do this is to use the results available so far.

In April 2006, two research institutes presented their final report on an investigation of substrates for the cultivation of young plants as part of the federal program for organic farming. Among other things, it was investigated whether arbuscular mycorrhiza in combination with (previously almost fungus-free) compost had positive effects on useful plants. The result at a glance:

  • Researchers recommend up to 40% compost for horticultural crops
  • Strawberries, lettuce, pelargonium, poinsettia and leek could be infected with AM fungi
  • Improvement of growth and flowering behavior of these plants
  • Contents of potassium, copper, phosphorus, nitrogen and zinc have increased in some cases
  • Peas benefited less
    • however, the root disease Pythium ultimum was suppressed in them
  • Species spectrum of AM fungi that were already in the ground was hardly changed by experiments
  • AM fungus strains bred by the University of Basel were able to promote plant growth more than the commercial preparations

As a result, the use of AM fungi in the almost fungus-free compost used was considered sensible, especially with strawberries and geraniums.

Different results in the test

A doctoral thesis from 2002 shows that the whole thing with the mycorrhiza is not that simple. It examined the influence of an arbuscular mycorrhizal fungus of the “Glomus intraradices” strain on the yield and nitrogen, phosphorus and potassium content of various herbs. Here basil, parsley, chives and tarragon were cultivated with and without mycorrhiza, once with mineral and once with organic fertilizer.

With mineral fertilization, more roots were colonized with mycorrhiza, but in the case of basil and parsley, neither the yield nor the nitrogen, phosphorus or potassium content changed with the mycorrhiza. Parsley responded to fertilizer form in yield but not to mycorrhiza. In the case of chives, the highest colonization rates were observed in the roots. In terms of yield, however, it also practically did not react to the mycorrhiza. Tarragon showed unclear and incomprehensible reactions to the mycorrhiza and the fertilizer forms. As a result, it was recorded here that the experiments could not meet the expectations of the mycorrhiza with regard to an increase in yield.

Obtaining the arbuscular mycorrhiza

Since the trade became aware of mycorrhizae, mycorrhizae have been cultivated and sold by many companies. It is not always said that exactly the fungus strain that actually benefits the respective plant is used, as the studies outlined above already indicate.

According to an article in the Swiss mushroom newspaper “Tintling” (Issue 1 from 2000, p. 24 ff.), mycorrhizae have only been researched since the mid-1980s, and it is difficult to assign mycorrhizae to the respective fungal species. Descriptions of mycorrhizae are still in their infancy. At that time, only 250 mycorrhizal forms were known, which is not really a lot with a (largely unexplored) total number of assumed 5 million fungi. Today there are already the first systematic collections of mycorrhiza in several European countries. One of them operates the z. B. Agroscope research institute in Zurich. In such collections, the researchers now examine each individual mycorrhiza to determine, among other things, which species form a nutrient network with which plants.

This work is really still in its infancy. However, the dealers usually offer you the mycorrhiza as if they knew exactly what each fungus does.

Of course, the freshness of the cultivation and the professional handling of the mushroom strains are also important. If you want to purchase and use mycorrhiza, it is best to contact a specialist who can tell you exactly and with justification which mycorrhiza is worth using for which plants and from which source.

apply mycorrhiza

But at least the application is quite easy once you find the right strain of mushroom. You simply mix 5 to 10 percent of the mycorrhizal-enriched substrate into whatever soil you are using. For potted plants, you can also sprinkle a spoonful of the mycorrhiza you bought on top of the soil and then work some in.

Symbiosis of fungi and plants

The mycorrhizal fungus provides the plant with nutrients and water. In return, he gets part of the assimilate from the plant that it produces through photosynthesis, up to a quarter goes to the fungus. As a mycorrhizal fungus, unlike other soil fungi, it does not have the enzymes it needs to break down complex carbohydrates and must therefore be supplied by the plant.

What the mycorrhiza can do better than the plant is extract minerals and water from the soil. It usually has a huge mushroom network. It also often improves the nitrogen supply and phosphate supply of its “hosts”, offers them protection against root pests and helps them to survive a dry period. So mycorrhiza and plant could really speak of a win-win situation.

Different functionalities

The ectomycorrhiza develop a fungal mycelium that covers the young root ends like a dense coat. They then swell in these areas and no longer form root hairs. In addition, ectomycorrhizae grow into the root bark. Here they do not penetrate into the root cells, but create a network in the spaces between the cells, which enables an exchange of nutrients between the fungus and the plant. The fungal roots take on the tasks that the root hairs would actually perform. Deep down into the soil, they ensure that their host has a good uptake of nutrients and water and protect it from pests.

The fungi that form the ectomycorrhiza as partners are mainly different pillar fungi. This also includes our boletes such as porcini mushrooms or chestnuts, agaricales, which include mushrooms, and sometimes sac mushrooms such as truffles. So most of the ectomycorrhiza are provided by our normal fungi that we know and collect to eat. In reality, however, they have much more extensive functions in the forest than just the formation of a profane fruiting body.

Endomycorrhizae proceed a little differently. A part of the fungal root network penetrates directly into the cells of the root bark of the corresponding plant partner. On the other hand, the endomycorrhiza do not form a network surrounding the roots like the ectomycorrhiza. In the cell of the root bark, the fungi now develop a kind of suction organ for nutrient absorption. They use this to deliver water and nutrients to their plant partner and absorb carbohydrates (sugar) from them.

The arbuscular mycorrhiza are a special form of the endomycorrhiza, precisely the form that forms arbuscules. These are particularly widely branched and delicate forms of spores (hyphae) that have a tree shape and develop within the root cells. However, most of the threads grow through the surrounding soil to provide the plant with good care. When researchers uncover mycorrhizal networks, huge interconnected systems appear.

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